Signal generator system



g- 12, 1952 M. K. GOLDSTEIN 2,607,034

SIGNAL GENERATOR SYSTEM Filed April 29, 1946 2 SHEETS-SHEET l H :ELEZL I2 I I0 l l \I TEST RECEIVER SIGNAL INPUT RECEIVER INDICATOR SOURCE omcuws ILE=E ToANTENNA IO l 2 IMPEDANCE TO ANTENNAII MATCHING DEVICE TO ANTENNA I2 l |7\ IT I Til IMPEDANCE w 23 MATCHING DEVICE TO RECEIVER INVENTOR. MAXWELL K. GOLDSTEI N ATTORNEY g- 12, 1952 M. K. GOLDSTEIN SIGNAL GENERATOR SYSTEM Filed April 29, 1946 2 SHEETS-SHEET 2 nvmvrm MAXWELL K. GOLDSTEIN ON 295% Av woz fio u @2502: w E MQZEMEE Y W F i mm mm m in N 2075mm A. $25085 M" mom 2206 @5522 323%? (.m Ill 5 W 3 2 zoiomw Av 325255 @2505: N mom EzQw M mm ill 823E; imm mm II E on mozmmzwo SE25 1 .2765

mm m WEWH A TT ORNE Y Patentecl Aug. 12, 1952 U-NlTED STATES PATENT OFFICE 13 Claims.

This invention relates "to signal generator devices and in particular to generator devices for producing signals having the characteristics of 'thosesignals derived from an incoming radio si nal wavefront by an antenna system of a radio direction finder system.

In radio direction finder antenna systems designed'to derive energysignals from an incoming wavefront to permit'a determination of the direction of arrival of the wavefront without ambiguity, special signal combining and resolving circuits must be employed. These circuits require accurate alignment which can only be achieved whensignals are simultaneously-applied thereto which bear the relationships which exist in the signals supplied by an actual antenna system. In many circumstances it becomes desirable to "align the input circuits independently of an antenna system. This is particularly true in the production line or the shop where the .uncertainties accompanying the reception of a signal from 'a distant source by an-antenna' system. cannot be tolerated. v

t is therefore an object of the present invention to provide .a signal generator system forproducing signal conditions .as would ein'st when receiving from a distant signal source by a con: ventional direction finder antenna or collector system.

Another .object of the present inventioniis to provide a'signal generator system capable of producing .a plurality of voltage signals having amplitude and phase relationships similar to those which would be produoedby a conventional direction finder antenna or collectorsystem when receiving froma distant station whose frequency may cccurat any point over a selected wide range of frequencies.

Another object ofthe present invention is to provide apparatus for determining the absolute 'performance'of radio direction finder systems.

Other and further objects .and features of the present-invention will ."become apparent .upon consideration of the accompanying description and drawings which illustrate typical features of the present invention.

Fig. 1 shows, partly in block, a typical radio direction finder system-to which the components of the'present invention have been 'afiixed.

Fig. '2 is a schematic diagram'showing the construction of the receiver input circuits as employed in the direction'finder system of Fig. 1.

Fig. 3 is a schematic diagram,'partly in block, of a signal generation system embodying the features of the present invention.

amended April 30, 1928; 370 O. G. 757) In accordance with the fundamental concepts of the present invention, a signal generator system is provided by which a plurality of signals bearing amplitude and frequency characteristics similar to those obtained from a radio direction finder collector or antenna system are produced. A conventional radio frequency signal generator is employed to produce a radio frequency signal which may be adjusted to any frequency in the band over which the radio direction finder is to operate.

To simulate the directional characteristics-of a direction finder antenna system, a :three element inductor systemi's employedinwhich power from the radio frequency signal source .is supplied to a first inductance. Second .and third inductances are positioned with their axes bearing angular mutual :relationships such-that the coupling to the-first inductance "will produce induced "voltages in the second and'thirdiinductances in amplitude ratio dependency on the angular orientation of the first inductance. This ratio may be adjusted by variation in the angular position of the first inductance to simulate different directions of arrival of incoming signals.

To simulate a sense input signal for the radio direction finder system a third signal is derived from the radio frequency signal in a manner independent of variationsinthe position-of the movable first "inductance. r

The amplitude of the output signals from the directional elements o'f-a directionfinder antenna system is, in general, greater at'higher frequencies than at low frequencies. Qver the usual frequencies employed in direction finder systems the output signals from the sense antenna are substantially independent of frequency. To simulate this frequency variation characteristic. a frequency-selective network {is provided ;in the signal generator system. This-selective'network maintains a definite vectorial (both magnitude and phase components) ratio between 'the resulta tude is independent of the direction of arrival of the wavefront. Output voltages from the anten nae I9, I I and I2 are applied through a switching device I3 to the receiver input circuits I4. The circuits I4 operate to eliminate the 180 ambiguity present in a figure-5 response pattern of a loop typesystem by combining the three antenna voltages to produce a single voltage of cardioid pattern whose amplitude is at a minimum or equal to zero only in one direction of incoming signal wavefront. The single combination signal from the receiver input circuits isthen amplified in a conventional receiver system i5 to facilitate a determination of the amplitude thereof. To facilitate this determination, a visual or aural indicator I6 is provided.

The collector system employing fixed crossed loop antennas ID and I I, each providing balanced output signals, may be replaced by other types of directional collector systems such as a single rotatable loop, or a single ro ta-table pair of vertical antennas (e. g. Adcocir. H-type), or two pair of fixed crossed vertical antennas (e. g. Adcock crossed-H) Methods by which the signals froma direction finder antenna system may be combined in the receiver input circuits I I to produce an output signal having a null in one direction are well known; A short description of a typical method is included here for reference.

In Fig. 2, receiver input components contained Within a shielding case are shown. Two fixed position inductances [1, I8 are employed to receive'ener'gy from the directional antennas Ill and II, respectively This received energy sets up inductive fields within the shielded enclosure which, because of the angular relationships of antennas II], II and inductances I'I, I8 may reproduce directional energy conditions similar to those existing in the vicinity of antennas II], II. A positionable inductance I9 absorbs a part of this energyfcr deliverance to the receiver I5. The amplitude and phasing of the voltage signal produced "across inductance IS with respect to the signals applied across inductances I7 and I8 depend upon the orientation thereof with respect to the inductances I'I, I8. For example, when the'longitudinal axis of inductance I9 is parallel to the longitudinal axis of inductance II, the voltage induced in inductance I9 is substantially in phase with and of an amplitude proportional to that impressed across inductance II.

The energy intercepted by inductance I9 is supplied through a coupling inductive arrangement including inductances I9-A and IS-B to the receiver I5. The signal thus developed across inductance IQ-B is supplemented by energy from inductance 29 derived from the sense antenna collector I2. The energy delivered to inductance I 9-3 from inductance bears vectorial relationship with respect to the energy delivered to inductance I 5-13 from inductance I9-A which may cause cancellation or reenforcement. In one angular position of the longitudinal axis of inductance I9 opposition of the signal components induced in inductance I9-B will exist. If the amplitudes of the components are equal, minimum output signal to receiver I5 will result. Such a condition is one which is desired in actual operation.

Impedance matching devices 2I, 2'2, 23 are provided to efi'iciently couple the signals applied to inductances I], I8 and 26 so that such a condition of amplitude equality may occur. Additional phase and amplitude compensating circuits are incorporated in impedance matching unit 23 (or 2I and 22) to permit proper phase and amplitude compensation of the energy from the directional and omnidirectional channels over the frequency range employed.

The primary purpose of the test signal source 24 is to produce signal components bearing the same amplitude phase'and frequency characteristics as those produced by an actual complete antenna system so that the impedance matching devices 2I, 22, 23 of the receiver input circuits I4 may be adjusted without requiring an actual antenna system. An additional purpose of the source 24 is to provide apparatus for determining the absolute performance of direction finding systems. This is accomplished by evaluating bearing accuracy and resolving power of the direction finders for various signal amplitudes, frequencies and apparent azimuth angles.

Typical features of the test signal source 24 are shown in detail in Fig. 3. A radio frequency signal, preferably unmodulated, is produced by the signal generator 25. It is desirable that the frequency and amplitude of this signal be adjustable so that the operational frequency and signal intensity ranges of the direction finder system may be covered. The output signal from the generator 25 is applied to a buffer-amplifier 26. The two variable amplitude components of an incoming signal as normally produced by the antennas II), II are simulated by a pair of inductances 21, 23 arranged with their longitudinal axes in a common plane but bearing quadrature positional relationship. Inductances 21, 28 are coupled to a third inductance 29 which may be positionable angularly through 360 degrees by means of an externally projecting control 29-A. The inductances 21, 28 may thus derive components of the Voltage applied across inductance 29 by amplifier 26 bearing amplitude relationships in dependency on the orientation of inductance '29. To prevent loading of the inductances by subsequent components, cathode follower amplifiers 30, 3I are placed in the output circuits thereof.

The output signal from amplifier 26 is also employed to derive a sense voltage to simulate the sense signal received by antenna I2. The transformer 35 and cathode follower amplifier 34 are employed in this circuit. To truly simulate the signals derived by a direction finder antenna system this sense voltage must bear certain frequency-amplitude and phase relationships with respect to the resultant of the signal components induced in inductances 27, 28. In conventional collector systems the resultant signal from the directional elements of the antenna, which must be opposed by the signal from the sense element in the receiver input circuits I I, has the characteristics of increasing amplitude withincreasing frequency. The output voltage from the sense element of the antenna system is substantially independent of frequency. To counteract this effect the impedance matching devices 2I, 22, 23 are provided with frequency selective elements. A frequency responsive network comprising resistance 32 and capacitance 33 is therefore employed in the simulator circuits to reduce the amplitude and control the phase of the signal applied to the cathode follower output amplifier 34 as the operating frequency increases. This network is chosen so that the magnitude of the resistance of element 32 is at least 10 times the capacitative reactance of element 33 at the highest frequency for which.

oneness operation .is intended. zelemerrts :and ithe voltage .ratio .of :the pouplingztransformer 335 are chosen {so that theiresultant of thesignals from the amplifiers 130,;3! bears thersameamplitude, phase and frequency relationships to the: signal from the :amplifier :34 :as exist between the .resultan't of the :signals. from antennas :I 0, H .and antenna l2 at :the f lowest frequencyfor which operation isdesireds =-Since the purposezof. the .generatingzsyst'em of Fig. :3 .is to provide signals for :the adjustment of the impedance matching elements 124, 2 2,. 2.3 of the ':receiver input .circuits, "it, is :necessaryithat the output impedance-of each, of the channels :from amplifiers 30, .31., 34 be equal,rrespectively, to the impedance :of the connections ate .:the :antennas H], II, l2. To this end, impedance matchingrsections 36, 3:1,,- -38- are :included 'so :thatra matched condition can beproduced; An additional purpose -of the matching sections 36,, 31, 38 .-is to transform 'thetunbalanced output :signalstof each of'the amplifierstll, 3i 34 -soithatthey will :appear as balanced (push-pull) signals :to simulate more closely the "actual output :of a balanced type collector system.

In a :permanent installation of 1a complete "di- 7 rection finder system it may be'desirable to connect the testsigna'l source :24 so that a :check of the system may he made, rapidly .and with as little :cablechanging as possible. :Ausw'itchde- This invention mayb'e u'sedor manufactured by v or for the Government of the United States for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. An artificial signal generating device to simulate actual signal reception conditions of a radio direction finder collector system, comprising: means producing oscillatory signals of variable frequency and amplitude, means deriving first and second components from said oscillatory r signals, means adjusting the relative amplitudes of the first and second related components to simulate different directions of signal reception, means deriving a sense signal component from said oscillatory signals independently of variations in relative amplitudes of the first and second components, and frequency responsive means varying the vectorial ratio of the resultant of the first and second signals to the sense signal component in a manner in dependency on the frequency of the oscillatory signals.

2. An artificial signal generating device to simulate actual signal reception conditions of a radio direction finder collector system, comprising: a local source for producing oscillatory signals of frequencies and amplitude similar to those of an actual signal, first positionable inductor means receiving energy from the local source, second and third inductor means deriving first and second related components of the signal applied to the first :inductor fin amplitude :ldependencyz-nn the -.orientation :of the first inductor, :means. deriving a :sensesigna-l component:fromrsaid'zosoillatory signals independently, of the "amplitude of the :first and second related components, sand :freguency mesponsive means varying-the vectorial ratio :otthe resultant of the .first and :second signals to the sense signal in dependency-onthe frequency of the oscillatqryrsignalsrin aemanner to i simulate the vectorial .ratios derived from th radio direction finder collectorisystem;

3. artificial :signal generating device gifor simulatingactual :signal reception Iconditi'ons 50f a. radio direction ifinder system having omnidirectional land;directional:collectorelements;loomprising: a local source producing oscillatory signals "adj ustablezato 'frequencies and amplitudesiin the range of operation of the direction .finder system, first and second' inductances positioned with their longitudinal axes in'one plane and mutuallyperpendicular, flzthil'd inductance magnetically linked -;to.Tthe firstfitwo inductancesqin an amount in dependency on the axial "orienta- .tion thereof with respect -to the .axi of ;each -of the first and second inductances inv theaforementioned plane, means positioning said third inductance "in the aforementioned ,rplane means applying thersignal fromasaid localssourceto-said third inductance, and a couplingnetwork derive ingindependently of the orientation of thejthird inductance -a:signa1 zfromisaid source bearing. the amplitude phase and .zfreguency characteristics relative to the resultant .of ;the.:signa 1s produced inthe :first and second inductances as, exist between :the energy fromrthe "omnidirectional collector :elements and :the resultant :of, the energy from. the J directional collector relementsgas :exist in .zan actual direction finder antenna system,

14.,3An .artificialxssignal generating; device ,to simulate actual ;signal 1 reception conditionsof a radio direction finder ccollector :system,;:icomprising: a local :source :producing oscillator-y signals of.freguencie iandamplitudes:similar .to thoseuof actual :s'ignal :sources, first. :andsecond inductances positioned "with. their longitudinal axes in onetplane and..-mutually perpendicular, a third inductance magnet'ically linked -;to the-first etwo inductances in the aforementioned plane, means positioning said third inductance in the aforementioned plane, means applying the signal from said local source to said third inductance, means derivin a signal from said signal source independently of the orientation of said third inductance, and a frequency selective system varying the vectorial ratio between the resultant of the signals induced in the first and second inductances and the signal derived by the last named means in a manner to simulate the vectorial ratios derived from the radio direction finder collector system.

5. An artificial signal generating device to simulate actual signal reception conditions of a radio direction finder collector system, comprising: means simulating received radio signals for producing oscillatory signals of variable frequency and amplitude, means for derivin first and second components from said oscillatory signals, means for adjusting the relative amplitudes of the first and second related components to simulate different directions of signal reception, and means for deriving a sense signal component from said oscillatory signals independently of variations in relative amplitudes of the first and second components,

6. An artificial signal generating device to simulate actual signal reception'conditions of a radio direction finder collector system comprisingza local source of radio frequency energy, means for deriving first and second components from said energy, means for varying the relative amplitudes of the first and second components to simulate difierent directions of signal reception, means for deriving from said energy a sense signal component independent of the amplitude variance of said first two components, and separate output circuits for said components.

7. In a calibrating arrangement for a radio direction finder system havin a'plurality of inputs for signals from a plurality of antennaethe combination with said system comprising: a local source of radio frequency energy, means for deriving from said energy a plurality of components simulating the antennae signals and means for separately impressing said components'upon the corresponding inputs of the system.

8. The combination of claim '7 further provided with means for selectively impressing said antennae signals or said locally generated components on the corresponding inputs of the system.

9. In a calibrating arrangement for a radio wave direction finder system having first and second inputs for separate signals derived from space quadrature antennae and a third input for a signal derived from a sense antenna, the combination with said system comprising: a local source of radio frequency energy, means for deriving first and second related components from said energy to simulate different directions of radio reception, means for adjusting the relative amplitudes of said first and second components, means for deriving a third component from said energy simulating a sense signal and means for separately impressing said three components uponthe three respective inputs of the system.

10. The combination ofclaim 9 further provided with means for selectively connecting said antennae signals or said locally generated components to the respective inputs of the system.

11. A multi-signal generator comprising: a sourceof radio frequency energy variable in frequency, means for deriving at least two component output signals from said energ separate output circuits for said signals and'means in one of said'output' circuits 'for varying in dependence on'a frequency variation a characteristic of one signal relative to the same characteristic of said other signal. a

12. A multi-signal generator comprising: a source of radio frequency energy variable'in frequency, means for deriving first and second component output signals fromsaid energy, means for varying the amplitude and sense of said first two signals, means unaffected by said signal variance for deriving a third component output signal from said energy, output circuits for said signals, and means varying in dependence on a frequency variation a characteristic of said third signal relative to the same characteristics of said other two signals. r J

13. A multi-signal generator comprising a source of radio frequency energy variable in frequency, means deriving from said energy first and second component output signals related in amplitude and sense as scalar sine and cosine components, means for varying the amplitude and sense of said first two signals in accordance with their relationship, means unaffected by said signal variance for deriving a third component output signal from said energy, and means for varying in dependence on a frequency variation the vector characteristic of said third signal relative to the vector'characteristics of said other two signals.

MAXWELL K. GQLDSTEIN.

REFERENCES CITED The following references are of record in the file of this patent; V

UNITED STATES PATENTS OTHER REFERENCES Alien Property Custodian application, Ser. No. 401,099, published May 25, 1943. 

